Source Heat Pump Water Heater Research Articles

Energy, exergy, economic, and environmental (4E) analysis of SAHP water heaters in very cold climatic conditions

Solar-assisted heat pumps (SAHPs) are emerging as promising solutions for space/water heating. Compared to conventional air-source heat pumps (ASHPs), SAHPs show superior thermal performance in cold climates where outdoor air temperatures are below freezing most of the heating season. However, given the inherent variability of solar energy, SAHPs have poor thermal performance to meet the load requirements during periods of weak solar radiation. To enhance the reliability of SAHPs, an air-source evaporator can be integrated with a SAHP, forming a dual SAHP – ASHP system with better performance. In this research, the energy, exergy, environmental, and economic performance of a dual-source solar/air source heat pump, which provides hot water for a typical Canadian household, is investigated. The performance of the system is compared with a solar-assisted direct-expansion heat pump (DX-SAHP), an ASHP, and conventional gas/electric water heaters. A thoroughly validated mathematical model based on heat transfer and thermodynamics fundamentals is developed and implemented in MATLAB® coupled with the CoolProp® library, which gives the refrigerant's properties. Results highlight the superior performance of the dual-source heat pump, particularly in the summer, where it surpasses the DX-SAHP. Among the examined heat pump configurations, the dual-source heat pump demonstrates the lowest annual power consumption. The system attains the maximum monthly average COP of 3.94 and achieves a minimum of 2.4 during the severe winter season in Calgary, Alberta. Compared to a conventional ASHP, the energy consumption of the system was reduced by 25%. The second-law analysis shows that the ASHP obtains the highest monthly average exergy efficiencies, followed by the DX-SAHP and the dual-source heat pump. Furthermore, results show that the solar/air source heat pump water heater can reduce CO2 emissions by 1450 kg/year, while the system's payback period is 19 years.

Experimental research on dynamic performance of an air/water source heat pump water heater

In this paper, a combined air/water source heat pump water heater is presented. At ordinary time, the heater can be used for hot water heating in water-source mode to improve the energy efficiency. While in cold season, it gives priority to air-source mode for water heating to improve operational safety. Experiments were conducted to investigate the thermodynamic performance of the heater in each operation mode, and the experiment results were analyzed. The research indicated that its operation was reliable during the long-time running. This paper offers a promising energy-saving method in future.

Solar-Air Source Heat Pump Water Heater for Scorching Climatic Condition: Energy, Exergy, Economic and Enviroeconomic (4E) Exploration for Sustainable Future

As solar-powered air source heat pump is an emerging water heating technique in scorching climatic conditions, it is necessary to explore their performance in terms of energy, exergy, economic, and environeconomic (4E) perspective. Henceforth, current research experimentally investigates and reports on 4E of Direct Expansion Solar-Air Source Heat Pump water heater for hot regions. A heat pump with a dual source evaporator is proposed in two working modes: solar air source mode and air source mode. The impact of ambient conditions on the thermal performance, such as power consumption, evaporator and condenser capacity, heating time, coefficient of performance, and exergy efficiency of the heat pump water heating system in both the working modes, was experimentally investigated. Results depict the coefficient of performance of the proposed heat pump system in solar air source mode and air source mode in the range of 2.37-5.05 and 2.26-4.21, respectively. On average, the system heating time in solar air source mode is 16.5% shorter than in air source mode. Based on the simulation results, compared to a conventional standard electric heating system, the payback period and lifetime carbon-dioxide mitigation savings cost of the proposed dual-source heat pump system are about 616 days and $179866, respectively.

Maximising the benefit of variable speed heat-pump water heater with rooftop PV and intelligent battery charging

Domestic applications of thermal energy storage, interacting with rooftop PV and batteries can substantially reduce consumer electricity costs, whilst assisting grid stability. Air source heat pump water heaters (HPs) with inherent thermal storage offer significant purchased energy savings, however, their typical control only considers stored water temperature. We demonstrate that further energy and cost reductions are possible using variable compressor speed controls that optimise thermal performance in real-time, whilst coordinating energy consumption to match available PV or shifting consumption to off-peak hours. The incremental complexity of variable-speed HP water heaters can reduce HP electricity consumption from the grid by up to 28% without PV or battery, 88% with PV, and 99% using PV and battery storage. By integrating the HP and all other domestic electrical loads, we exploit the combination of thermal and battery energy storage using rules-based and machine-learnt hierarchical controls to reduce the net household energy cost. Machine-learnt grid battery charging is shown to reduce annual grid energy consumption by 84%, delivering 99% of the potential energy cost savings. We conclude that a HP with inherent thermal storage, interacting with rooftop PV offers the most cost-effective home energy storage solution, lowering net lifetime costs by up to 27%.

Experimental study of air source heat pump water heater: Energy, exergy, and entransy analysis

Experimental study of air source heat pump water heater: Energy, exergy, and entransy analysis

Performance and Optimization of Air Source Heat Pump Water Heater with Cyclic Heating

Performance and Optimization of Air Source Heat Pump Water Heater with Cyclic Heating

Long-Term Performance Analysis of Direct Photovoltaic Thermal-Assisted Heat Pump Water Heater Using Computational Model

The photovoltaic thermal system has a limitation in supplying hot water at the required temperature since it requires a supplementary heating system. One such system can be an air source heat pump operated by electricity from a PV/T system, which can be used to raise the temperature of the water preheated by PV/T to the required level. Such type system can also be called a hybrid PV/T-heat pump system, and it delivers thermal (hot water) and electrical energy. The performance of the hybrid PV/T-heat pump system was analyzed using the computational model for two Ethiopian cities, namely, Addis Ababa and Dire Dawa, which represent the highland and lowland regions, respectively. The simulation was conducted by inputting climatic data, daily hot water demand, and hourly hot water consumption patterns. Also, system design parameters such as PV/T area and peak Watt, PV/T warm water tank volume, air source heat pump water heater COP as a function of ambient temperature and circulating water temperature, and heat pump hot water tank volume. Besides, the effect of hot water consumption patterns (variability effect in three dissimilar cases constant, restaurant, and motel) on the system performance was examined. In addition, the effect of electric energy supply to the compressor of the heat pump using battery storage on the system performance was also investigated. In those diverse situations, the system in most of the cases generated hot water above 55°C and scored a COP of 3. The maximum value of hot water end-use efficiency of 66% was also obtained by making the hot water tank capacity about 50% of the daily hot water consumption size.

Energy, exergy, economic and environmental analysis of photovoltaic/thermal integrated water source heat pump water heater

The photovoltaic thermal integrated water source heat pump (PV/T-WSHP) water heater system can meet the demand for not only the domestic hot water but also the electricity production. To comprehensively analyze the benefits of the PV/T-WSHP water heater system, energy, exergy, economic and environmental analysis method was applied. A TRNSYS model of the PV/T-WSHP water heater system was developed based on the existing experimental setup, and validated by the experimental data. A combined system of single PV system and single air source heat pump water heater (PV + ASHP) system model was also built for comparison. The simulated results indicated the PV/T-WSHP water heater system had a 25.3% improvement in electrical conversion efficiency, a slightly lower EER of 3.71 and a significant reduction in annual exergy loss, comparing with the combined PV + ASHP system. In addition, the annual cost of the PV/T-WSHP water heater system was 217.7 yuan lower than the combined PV + ASHP system. The PV/T-WSHP heat water system and the combined PV + ASHP system could annually save the standard coal of 0.62 tons and 0.50 tons, respectively. This study provides an effective method to comprehensively analyze the performance of the PV/T-WSHP water heater system.

Using statistical tests to compare the coefficient of performance of air source heat pump water heaters

The study compared the coefficient of performance (COP) of two residential types of air source heat pump (ASHP) water heaters using statistical tests. The COPs were determined from the controlled volume of hot water (150, 50 and 100 L) drawn off from each tank at different time of use (morning, afternoon and evening) periods during summer and winter. Power meters, flow meters, and temperature sensors were installed on both types of ASHP water heater to measure the data needed to determine the COPs. The results showed that the mean COPs of the split and integrated type ASHP water heaters were 2.965 and 2.652 for summer and 2.657 and 2.202 for winter. In addition, the p-values of the groups COPs for the split and integrated type ASHP water heaters during winter and summer were 7.09 x 10-24 and 1.01 x 10-11, based on the one-way ANOVA and the Kruskal-Wallis tests. It can be concluded that, despite the year-round performance of both the split and integrated type ASHP water heaters, there is a significant difference in COP at 1% significance level among the four groups. Furthermore, both statistical tests confirmed these outcomes in the comparisons of the mean COPs among the four groups based on the multiple comparison algorithm.

FEASIBILITY STUDY OF NET-ZERO ENERGY RESIDENTIAL BUILDINGS IN HOT AND HUMID CLIMATES: A CASE STUDY OF IRAN

The use of solar energy in buildings is a good alternative to fossil fuels considering the geographical location of Iran. The present research evaluated the feasibility of net-zero energy residential buildings in southern Iran using a distinct framework. To this end, a low-energy and simulated model of a multi-family residential building as the dominant typology in Bushehr city equipped with combined (active and passive) solutions were used in Design Builder software for optimizing energy consumption. Annual electricity consumption of this simulated model was reduced by 48% using very low power density appliances and an Air Source Heat Pump (ASHP) water heater with an Energy Star label to supply hot water. Then, a grid-connected PV system with a capacity of 29 kW was used to provide the annual electricity demand. The results indicate that this system annually generates 52 MWh of electricity that not only covers the annual electricity demand but also sends 5.8 MWh of additional electricity to the grid. The Economic analysis indicates that the payback period in this project will be very long. Therefore, achieving NZEBs in southern Iran is technically feasible but, from the economic point of view, it depends on the provision of the economic infrastructures.

A modified exergy analysis method for vapor compression systems: Splitting refrigerant exergy destruction

To locate the major imperfections and determine the optimization directions for developing high-efficiency vapor compression systems, a modified exergy analysis method is proposed in this study. In contrast to previous exergy analysis methods, the proposed method can split the exergy destruction of the refrigerant and simultaneously exhibit exergy destructions of the refrigerant and other components, which makes the optimization more effective. The modified exergy analysis is compared with other exergy analysis methods by analyzing and optimizing an air source heat pump water heater. As a result, the optimization of a typical air source heat pump water heater based on the modified exergy analysis method achieves a coefficient of performance improvement of over 17.0–27.5% compared to other exergy analysis methods. Finally, the modified exergy analysis method is used to optimize an actual high-efficiency inverter room air conditioner. The optimization directions are clarified. Improving the energy efficiency of the compressor and decreasing the refrigerant exergy destruction are identified to be the key factors for optimization.

Investigating heat transfer and frosting performance of air source heat pumps with the impact of particulate fouling

Due to superior energy efficiency and emission-reducing potential, air source heat pumps (ASHPs) have been widely used in space heating and domestic water heating. However, the heating seasons usually coincides with the serious air pollution, hence particulate fouling appears on ASHPs' outdoor coils repeatedly, despite being de-fouled periodically. In this study, four levels of fouling, namely none fouling (0 g/4 m2), mild fouling (15 g/4 m2), moderate fouling (40 g/4 m2) and severe fouling (70 g/4 m2), were concretized on a finned tube heat exchanger successively, followed by experimentally investigating the negative effects of fouling on the heat transfer performance of an air source heat pump water heater (ASHPWH). Results demonstrated that the effects of fouling on the performance of ASHPs in heating mode would be exacerbated with decreased air temperature. In addition, the frosting performances at different levels of fouling were evaluated quantitatively, by depicting the frosting evaluation plots. The frosting evaluating plots suggested that fouling would expand the air temperature and relative humidity (RH) ranges where frosting appears, and would hasten frosting process. As verification, signal factor experiments were carried at different levels of fouling. The experimental results confirmed that the increase of fouling level would result in faster frosting process, but smaller final frost accumulation mass.

Analysis and optimization on the performance of a heat pump water heater with solar-air dual series source

Heat pump water heater can economize dramatic amounts of energy in domestic application. To make full use of hybrid heat source, a solar-air dual series source heat pump water heater (SA-HPWH) is proposed. The refrigerant can get vaporized in two types of evaporators to adjust to variable working conditions. Based on distributed modeling approach, the dynamic model of SA-HPWH system is established. The operational characteristics of the SA-HPWH system have been discussed under different working conditions. The results show that the SA-HPWH system is able to work effectively under low solar irradiation and ambient temperature. The average COP rises from 2.23 to 2.63 with Tair rising from 10 °C to 20 °C. The rise in solar irradiation can lift the evaporating capacity of collector evaporator, while the value in air source evaporator decreases. The overall performance can be enhanced by rising G, and the average COP increases from 2.23 to 2.40 with G increasing from 100W/m2 to 500W/m2. The rise of wind velocity can enhance heat transfer at air side, as well as COP, but the impact is not significant with the wind velocity exceeding 3m/s. In addition, the performance of the SA-SHPWH system can be further improved by utilizing PV/T collector.

Research on the characteristics of the refrigeration, heating and hot water combined air-conditioning system

Air source heat pump (ASHP) and heat pump water heater (HPWH) have the advantages of convenience and high efficiency. The newly proposed refrigeration, heating and hot water combined air-conditioning system (RHHAC) combines traditional ASHP with HPWH. The demands of users for cooling, heating and hot water are effectively satisfied with this equipment. In this study, five groups of experiments were conducted to study the starting and operating characteristics of the system. Besides, two sets of experimental cases were carried out to explore the operating characteristics of the system under the frosting process. Results show that the maximum superheat degree is 11°C when the system starts in hot water mode, while the maximum superheat degree is more than 22°C when the system starts in the other modes. As the temperature of hot water rises when the system runs in hot water mode, the maximum value of the discharge pressure can reach 3.7MPa. Besides, the analysis parameters will have regular pulsations when the system is in cooling mode. For example, in the experimental case 5, the fluctuation range of the superheat degree is 5.1°C-16.2°C.

Model predictive control for the operation of a transcritical CO2 air source heat pump water heater

This paper presents a model predictive control (MPC) approach to optimize the operation of a transcritical CO2 air source heat pump (ASHP) water heater. Past findings have revealed that the heat rejection pressure is the key factor affecting the system performance of the ASHP. However, the currently used PI controls based on correlations and other control strategies reported in the literature have some limitations. In this paper, we applied the MPC strategy in an ASHP water heater to optimize its operational performance in real-time. Different from the current control strategy aiming to search for the optimal heat rejection pressure, MPC predicts the future operation condition and calculates the optimal inputs based on the control-oriented model and objective function. A high-fidelity physical model is first built in Dymola to produce the operational data, then a data-driven control-oriented model for MPC is derived from the data source via a dynamical system identification. MPC is designed to maximize the coefficient of performance of the ASHP water heater under the state-space equations and constraints. The evaluation is carried out under several cases including fixed ambient temperature, realistic ambient temperature, and variable water outlet temperature. The simulation results prove the control effectiveness of MPC.

Pathways for decarbonizing China’s building sector under global warming thresholds

To achieve the long-term climate targets of limiting global warming to well below 2 ℃ and 1.5 ℃ relative to pre-industry levels, China’s building sector must be deeply decarbonized considering its potential of substantial emissions increase. However, how to deploy the energy technologies and how much we need to pay for China’s building sector for achieving the global warming targets remain unknown. Here, we develop a bottom-up national energy technology model for building sector (NET-Building) to explore the optimal energy technology pathways, energy demands as well as costs and benefits for decarbonizing China’s building sector under 2 ℃ and 1.5 ℃ targets. The results show that to meet the 2 ℃ target, most of fossil fuel-fired end-use devices and all traditional biomass-fired end-use devices need to be significantly reduced for the whole building sector. To pursue a more aggressive 1.5 ℃ climate goal, both proportions of the ground source heat pump and solar thermal water heater need to be drastically boosted and reach 100% in commercial sector by 2050. The decarbonization of China’s building sector under 2 ℃ and 1.5 ℃ targets can obtain 44 and 137 trillion CNY net incomes until 2050, respectively.

Linear Regression Analysis and Techno-Economic Viability of an Air Source Heat Pump Water Heater in a Residence at a University Campus

This study quantifies the potential of a 4.0 kW air source heat pump (ASHP) unit retrofitted to a 12.0 kW, 1000 L electric boiler coupled to a 1000 L storage tank. A data acquisition system was built to monitor the performance of the electric boiler and the ASHP water heater. The annual electrical energy saving and the load factor reduction from the electric boiler because of the ASHP unit retrofit was 34,805.94 kWh and 0.124. The net present value payback period of the ASHP system was 1.60 years. A Wilcoxon rank sum test was employed to compare both the volumes of hot water and electrical energy consumed by the two systems. Linear regression models of the daily volumes of hot water and electrical energy consumed by both systems were established. The results should be of great value to the management of universities that are considering energy-efficient interventions with a significant return on investment.

Experimental Investigation on an Ultra-High Temperature Air Source Heat Pump Water Heater

Abstract To generate boiling water beyond 100 °C via heat pump technology, the prototype of an ultra-high temperature air source heat pump water heater (ASHPWH) based on a single-stage compression cycle of R134a was established, and an experimental investigation on it was conducted under an environment temperature of 25 °C. Then, thermodynamic analyses were carried out on the basis of the experimental results, especially when the prototype produced 95.9 and 100.3 °C water. The experimental and analytical results indicate that water beyond 100 °C was achieved through the prototype. When producing 100.3 °C water, the discharge temperature and compression ratio of the compressor of the prototype are only 108.4 °C and 4.07, respectively, which are in moderate levels. Correspondingly, the work input of the compressor is 0.622 kW, the heating capacity is 2.786 kW, and the heating coefficient of performance is 4.48. In addition, when producing 95.9 and 100.3 °C water, the system exergy efficiencies of the prototype are 50.76% and 49.73%, which are larger than those of the existing ASHPWHs, demonstrating that dividing the condensing process into two parts of high-grade exergy and low-grade exergy and utilizing them separately is effective. That is the essential reason of generating boiling water beyond 100 °C as expected only through the single-stage compression cycle.

Energy, economic and environmental assessment of transcritical carbon dioxide heat pump water heater in a typical Chinese city considering the defrosting

Considering the high demand for domestic hot water in China, the air source heat pump water heater is being popular due to higher energy efficiency. However, the heat pump is mainly studied from the energy perspective in the previous literature, and the influence of the frosting is also neglected. In this paper, with the presented domestic hot water load in a typical Chinese city, the carbon dioxide heat pump was tested at the varied ambient temperatures considering the different defrosting methods. With the proposed hot gas bypass defrosting method, a techno-economic analysis is required. To show the benefits of the proposed system, the unit is analyzed with the energy, economic and environmental analysis. The comparison with two traditional heating solutions is also presented. Results show that the seasonal performance factor is improved by 2.85%, and the annual fuel cost is decreased by 758.26 Chinese yuan in the proposed system compared with the baseline system. For the additional cost required by the proposed defrosting method, the proportion declines rapidly from 1.53% to 0.46% in the first 5 years. Compared with the direct electric heater, the life cycle cost is reduced by 2313.23 thousand Chinese yuan, and the carbon dioxide emission is declined by 266.46 tons in the proposed system. With the negligible direct emissions of 36.98 kg, the total equivalent warming impact is mainly determined by the indirect emissions. The primary energy consumption and CO2 pollutant emission is related with the domestic hot water load. The payback period is sensitive to the domestic hot water load, compressor cost and electricity price.

Evaluation of the coefficient of performance of an air source heat pump unit and an air to water heat pump

Air source heat pump (ASHP) water heaters are efficient devices for sanitary hot water heating. The coefficient of performance (COP) of the air to water heat pump (AWHP) is constantly lower than that of the corresponding ASHP unit. The study focused on determining the COP of both the ASHP unit and the AWHP. This was achieved by the implementation of both experimental and simulation methods, with the help of a data acquisition system and the REFPROP software. The system comprised of a 1.2 kW split type ASHP unit and a 150 L high pressure geyser. A power meter, flow meters, temperature sensors, pressure sensors, ambient temperature and relative humidity sensor were installed at precise locations on the split type AWHP. Controlled volumes of 150, 50 and 100 L were drawn off from the AWHP during the morning, afternoon and evening for a year. The average COP for the summer and winter, in terms of the input electrical and output thermal energies of the AWHP were 3.02 and 2.30. The COPs of the ASHP unit, in terms of the change in the enthalpies of the refrigerant at the inlet and the outlet of the condenser and the evaporator, were 3.52 and 2.65 respectively. The study showed that the difference between the COP of the ASHP unit and that of the AWHP could be ascribed to the electrical energy consumed by the fan and the water circulation pump during the vapour compression refrigeration cycles. The work provides an energy optimisation opportunity to the manufacturers of this technology, helping to enhance the efficiency and COP of ASHP water heaters.
 Highlights
 
 The COPt of the ASHP unit was higher than the COPe of the AWHP.
 The COPe of the AWHP was the ratio of the input electrical energy consumed and the output thermal energy gained by the stored water.
 The COPt of the ASHP unit was enthalpies-dependent and a function of inlet and outlet enthalpies of the evaporator and condenser.
 The inlet and outlet refrigerant temperatures profiles of the condenser confirmed thermal energy dissipation.